| 西沙群岛石岛浅部基底地壳应力测量及其地球动力学意义分析 |
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| 引用本文： | 张重远,王振峰,范桃园,侯春堂,付长垒,区明益,汪西海,陈群策.西沙群岛石岛浅部基底地壳应力测量及其地球动力学意义分析[J].地球物理学报,2015,58(3):904-918. |
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| 作者姓名： | 张重远 王振峰 范桃园 侯春堂 付长垒 区明益 汪西海 陈群策 |
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| 作者单位： | 1. 国土资源部新构造运动与地质灾害重点实验室, 北京 100081;
2. 中国地质科学院地质力学研究所, 北京 100081;
3. 中海石油(中国)有限公司湛江分公司, 广东 湛江 524057;
4. 中国地质科学院地质研究所, 北京 100037 |
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| 基金项目： | 中国重点海域地应力观测及综合研究(1212011220122)资助. |
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| 摘 要： | 西沙群岛独特的构造位置决定了其构造运动背景和地壳应力场动力源的复杂性.位于西沙群岛石岛、深达1268.07m的西科1A井在1257.52m钻遇花岗岩基底.在1125.8~1262.0m开展5次水压致裂地应力测量,获得最大水平主应力为17.09~20.85MPa,最小水平主应力为15.97~18.29MPa,估算垂直主应力为22.86~26.68 MPa,地壳应力结构为SVSHSh,以垂直主应力为主导,该应力结构特征有利于正断层活动,表明西沙群岛地壳基底处于拉张的应力环境.受西沙海槽断层影响,水平应力值较低.印模测试显示基底地壳应力方向以近东西-北西向为主,与已有的GPS测量、横波分裂和面波反演结果较为吻合,显示西沙群岛岩石圈尺度上变形一致性较好.西沙群岛地壳应力场的力源受板块运动和地幔物质上涌作用联合制约.综合南海西北部实测地应力数据分析,显示该区域主应力方向较为一致,应处于统一、稳定的构造运动背景之中.西科1A井水压致裂试验是我国首次涉海深孔地壳应力测量,具有重要的地球动力学意义,提供了研究南海地球物理场的宝贵基础资料.
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| 关 键 词： | 西科1A井 浅部基底 水压致裂应力测量 地球动力学意义 西沙群岛 南海西北部 |
| 收稿时间： | 2014-10-08 |
Crustal stress measurement in shallow basement of Shidao of Xisha Islands and analysis of its geodynamic significance |
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| ZHANG Chong-Yuan,WANG Zhen-Feng,FAN Tao-Yuan,HOU Chun-Tang,FU Chang-Lei,OU Ming-Yi,WANG Xi-Hai,CHEN Qun-Ce.Crustal stress measurement in shallow basement of Shidao of Xisha Islands and analysis of its geodynamic significance[J].Chinese Journal of Geophysics,2015,58(3):904-918. |
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| Authors: | ZHANG Chong-Yuan WANG Zhen-Feng FAN Tao-Yuan HOU Chun-Tang FU Chang-Lei OU Ming-Yi WANG Xi-Hai CHEN Qun-Ce |
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| Institution: | 1. Key Laboratory of Neotectonic Movement & Geohazard, Ministry of Land and Resources, Beijing 100081, China;
2. Institute of Geomechanics, Chinese Academy of Geological Science, Beijing 100081, China;
3. CNOOC China Ltd. Zhanjiang, Zhanjiang Guangdong 524057, China;
4. Institute of Geology, Chinese Academy of Geological Science, Beijing 100037, China |
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| Abstract: | In order to understand the stress field characteristics and carry out geodynamic study of South China Sea, the Xike 1A well, located in Shidao of Xisha Islands was drilled for hydraulic fracturing in situ stress measurement. Using in situ stress test results in shallow basement of Shidao of Xisha Islands, combined with other geophysics data, the geodynamic background and force source of basin expansion are analyzed. In situ stresses were measured by using hydraulic fracturing method with the standard equipment and procedure suggested by International Society for Rock Mechanics (ISRM). The critical pressure parameter, shut-in pressure (Ps), was processed and determined with the single tangent method, dp/dt method, dt/dp method, and Muskat method. The orientation of the maximum horizontal principal stress was determined by impression technique. Additionally, some representative rock specimens from the 1153.14~1267.5 m were selected to make rock thin sections for observation and determination of rock microstructure and characteristics near the shallow basement.The 1268.07 m-deep Xike 1A well revealed an about 1257.52 m-deep sedimentary cover that mainly consists of bioclastic limestone, marbleized limestone, and dense sedimentary marble, and reached the shallow basement which consists of quartz diorite and granite. In this borehole, we conducted hydraulic fracturing stress measurements at 5 depth intervals between 1125.8~1262.0 m, and obtained the maximum horizontal principal stresses of 17.09~20.85 MPa, the minimum horizontal principal stresses between 15.97~18.29 MPa, and the estimated vertical principal stresses between 22.86~26.68 MPa. The feature of crustal stresses is SV>SH>Sh and the vertical principal stress plays a dominant role, which is prone to the activity of normal fault. Influenced by faults around the Xisha Trough, crustal stress level is relatively low. Impression tests show that the orientations of the maximum horizontal principal stresses in basement of Xisha Islands are from nearly EW to NW. The dominant direction, NWW, coincides well with existing GPS measurements, shear wave splitting measurements, and surface wave inversion data, which show the well consistency of lithosphere deformation of Xisha Islands. The feature of crustal stress implies that the crust basement of Xisha Islands is in an extensional stress environment. Crustal stress field here is jointly constrained by plate movements and upwelling of the Earth's mantle material of Northwestern South China Sea. Analysis from measured in situ stress data of Northwestern South China Sea indicates that the regional principal stress orientations are similar and hence, this region is during in a uniform and stable background of tectonic movement. |
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| Keywords: | Xike 1A well Shallow basement Hydraulic fracturing stress measurement Geodynamic significance Xisha Islands Northwestern South China Sea |
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